• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.5
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• pp.622-630
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• 2010

The increase of the spindle speed to enhance the productivity in ring spinning processes has been limited by yarn tension and heat generation of the traveller/ring. The main causes of yarn tension are 1) the force added directly to the yarn by the rotation of the spindle and 2) the centrifugal force exerted by the yarn balloon generated by traveller rotation. The dominant causes of heat generation are 1) the friction between the ring and traveller and 2) the friction between the traveller and yarn. These factors cause yarn end-breaks and heat damage. In the case of the staple yarn manufacturing process for PET (polyester) and nylon (a heat plasticity material), the rotational speed of the ring spinning system has deteriorated to 10,000rpm. The objective of this study was to develop a rotating ring which has dynamic stability, high productivity and a simple structure to overcome the limitations of the conventional fixed ring/traveller system. The results of this study revealed that the spinning tension could be reduced by 67.8% using the newly developed rotating ring.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.98-104
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• 2007

The carbon fiber reinforced carbon composite (CFRC) materials are necessary for the advanced industries that require the thermal resistance. And the development and research for CFRC has been in progress in the field of aerospace and defense industry. CFRC have several advantages and special properties such as excellent anti ablation, outstanding strength retention at very high temperature, high heat capacity and thermal transport, high specific stiffness and strength, and high thermal shock resistance. They have been used as aircraft brake, rocket nozzle, nose cones, jet engine turbine wheels, and high speed craft. Since the technology related to CFRC was prohibited from importing and exporting, we developed our own technology to produce F-16 B32 brake disk made out of CFRC, and then we performed various tests to observe the characteristics of CFRC-based brake disk developed in this study in view of density, strength, friction, specific heat, and heat conductivity.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.341-349
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• 2001

Heat distortion of the non-contacting mechanical face seal is affected by friction heat between primary seal and seal sheet. The fluid or gas in mechanical face seal maintains operating gap, cooling friction heat and lubricates at the face of seal. So we designed face of seal for inclined face. inclined face of seal improves fluid or gas flow at the face of seal and it increases circumferential velocity at outer radius of the seal so temperature of the seal is decreased by low heat transfer coefficient at there. In this paper, inclined face seal are analysed numerically using finite element method for proof improve inclined face seal performance. Angle of the incline face used for FEA is from 50$^{\circ}$to 90$^{\circ}$and for explaining the effects of inclined face in seal, we get temperature, face distortion, and stress in the seal with variable operating gap and rotating speeds. Result of analysis shows that angle of the incline face is 60$^{\circ}$come to good thermal distortion characteristics.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.88-98
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• 1996

The present study is concerned with the flow friction and heat transfer characteristics of the combination of various regenerator materials, using the different Darcy number and porosity, which is filled uniformly and partially in a tube under oscillating flow condition. The poros medium is adopted as Brinkmann-Forschheimer extended Darcy model. Numerical results are obtained or the flow and temperature fields and described the effect of the combination of various regenerator materials and Womersley number on the pressure drop, the heat transfer and the regenerator efficiency. The results obtained indicate that not only heat transfer between the tube wall and oscillating flow but also the pressure drop at both ends of the regenerator are increased, while the regenerator efficiency is decreased in the increase of womersley number. It is also found that the friction factor is increased as Reynolds number is increased. The comparison between the combination of the various regenerator materials and the homogeneous regenerator material shows that the regenerator efficiency can be enhanced with the proper combination of various regenerator materials even though the averaged porosity of the regenerator is same.

• The KSFM Journal of Fluid Machinery
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• v.18 no.1
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• pp.29-36
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• 2015

Recently, Stirling engines are emerging as a key device for power conversion of renewable energy or waste energy. This study develops a LTDSE(Low Temperature Differential Stirling Engine) using a water spray for higher heat transfer and performs load performance tests for various flow rates and temperatures of hot water spray for variable engine loads emulated by a mechanical friction device. Internal temperature and pressure, working frequency and inlet and outlet temperature of the supply water are measured. As a result, the increases in flow rate and temperature of hot water respectively enhance the power output, efficiency and the working frequency, while the increasing engine load leads to decreases in working frequency but increases in the pressure amplitude. Eventually, it is revealed there exists a maximum shaft power of the test engine.

• Design & Manufacturing
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• v.15 no.3
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• pp.7-12
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• 2021

Plastic injection molds used for rapid heating and cooling must minimize surface damage due to friction and maintain excellent thermal and low electrical conductivity. Accordingly, various surface treatments are being applied. The properties of Al₂O₃ coating and DLC coating were compared to find the optimal surface treatment method. Al₂O₃ coating was deposited by thermal spray method. DLC films were deposited by sputtering process in room temperature and high temperature PECVD (Plasma enhanced chemical vapor deposition) process in 723 K temperature. For the evaluation of physical properties, the electrical and thermal conductivity including surface hardness, adhesion and wear resistance were analyzed. The electrical resistance of the all coated samples was showed insulation properties of 24 MΩ/sq or more. Especially, the friction coefficient of high temp. DLC coating was the lowest at 0.134.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.434-441
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• 2016

Friction Stir Welding (FSW) is a solid-state joining process involving the frictional heat between the materials and tools. The amount of heat conducted into the workpiece determines the quality of the welded zone. Excessive heat input is the cause of oxides and porosity defects, and insufficient heat input can cause problems, such as tunnel defects. Therefore, analyzing the temperature history and distribution at the center of the Friction Stir Welded zone is very important. In this study, the temperature distribution of the friction stir welding region of an AZ61 magnesium alloy was investigated. To achieve this goal, the temperature and metal flow was predicted using the finite element method. In FE analysis, the welding tool was simplified and the friction condition was optimized. Moreover, the temperature measuring test at the center of the welding region was performed to verify the FE results. In this study, the tool rotation speed was a more dominant factor than the welding speed. In addition, the predicted temperature at the center of the welding region showed good agreement with the measurement results within the error range of 5.4% - 7.7%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.762-771
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• 1987

Friction welding is a fusion process in which the necessary heat is generated by clamping one of the two pieces to be welded in a stationary chuck and rotating the other at high speed with an axially applied load. It is essentially a variation of the pressure welding process but utilizes a novel heating method. In addition to the foregoing advantages, it has also been reported excellent for welding dissimilar materials. Therefore, this study reported on investigating the strength behavior for the frictionally welded domestic structural steel SM45C and SUS304. The results obtained by the experiments are as follows. (1) The highest tensile strength of the best friction welded specimen (B4) is about 3% lower than that of SM-45C base metal, and 9% lower than that of SUS304 base metal. The heat treated specimens (850.deg.C 1hr A.C) have almost same value of tensile strength. (2) The strain of SM45C base metal is 27.3% and that of SUS304 is 42%, that of the best friction welded specimen (B4) appeared as 11.9% which is about 50% lower than the base metal, so, this same phenomenon apeared in all the other welding conditions. (3) The bending strength of SM45C base metal is 123kgf/mm$^{2}$ and that of SUS304 is 127kgf/mm$^{2}$. The best specimen (B4) appeared as 121kgf/mm$^{2}$ which is almost same bending strength for both base metals. (4) The friction welded condition involving maximum strength is determined by P$_{1}$=8kgf/mm$_{2}$, P$_{2}$=22kgf/mm$_{2}$, T$_{1}$=10sec, T$_{2}$=2sec, and amount of upset 7.6mm. (5) The interface of two dissimilar materials are mixed strongly, and welded zone is about 1.03mm and also the heat affected zone is about 2.36mm at SM45C while about 1.85mm at SUS304, therefore the welded zone and heat affected zone are very narrow to compare with those of the other welding materials.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.783-789
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• 2012

In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.

• KSTLE International Journal
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• v.1 no.1
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• pp.63-68
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• 2000

Angular contact ball bearings are mainly used in the spindle, which requires high speed and stiffness. The heat generation is studied by experiments and simulations using a pair of angular contact ball bearings. The temperature variation of inner and outer races and the temperature increment distribution are measured by using thermocouples for the rotational speed, preload, viscosity of lubricant. The measured values from experiments are used to estimate the heat conduction rate. The method of oil-air lubrication is used for the experiment. The amount of conduction heat transfer to the test spindle and the convection heat transfer coefficients long the spindle are computed by using inverse method with temperature increment distribution. Total heat generation rate is estimated with the heat partition rate which is calculated from temperatures of inner and outer races. In addition, the empirical factor of oil-air lubrication method for Palmgren's heat generation model is suggested. The empirical friction coefficients, which are obtained from the experiments, depend on the preload condition, and can give us more accurate estimation of the heat generation in ball bearings.