• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.189-190
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• 2002

Rolling-sliding friction was investigated for three SBR (styrene-butadiene rubber) specimens including silica-filled, HAF carbon black-filled, and SAF carbon black-filled SBR. When a rubber wheel was rolled against a glass disk, the coefficient of friction varied with the slip ratios. The coefficient of friction for the silica-tilled SBR showed the highest value of the rubber specimens examined under various slip ratios. The contact areas of silica-filled SBR were larger than those of the carbon black-filled SBRs, as indicated the modulus of the silica-filled SBR showing the lowest value. The contact area during rolling-sliding friction was always smaller than those during the static contact. The friction force at the unit contact area for the silica-filled SBR under braking and driving was higher than those of carbon black-filled SBRs.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1030-1041
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• 1997

The control model in the tandem cold rolling mill consists of many mathematical theories and is used to calculate the reference values such as the roll gap and the rolling speed for good operation of rolling mill. But, the control model used presently has a problem causing inaccurate prediction of the rolling force. By the parameter identification, it was found that the main factor causing inaccurate prediction of the rolling force was incorrect modeling of the friction coefficient and the flow stress. To get rid of the erroneous factor new adaptive schemes are suggested in this work. Those are a long-time adaptation by the iterative least-square method and a short-time adaptation by the recursive weighted least-square method respectively. The new equations for the friction coefficient and the flow stress are derived by applying the suggested adaptive algorithms. Through the on-line test in an actual mill, it is proved that the rolling force predicted by the new equations is more accurate than the one by the existing equations ever used.

• KSTLE International Journal
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• 제9권1_2호
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• pp.17-21
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• 2008

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present study is one of studies to maximize the advantages of refrigerant compressors. In addition, because friction characteristics of the critical sliding component is essential in the design of refrigerant compressors, the present study also analyzed the lubrication characteristics of a rotary compressor used for refrigeration and air-conditioning systems. In order to measure the friction force between the vane and the rolling piston, an experimental apparatus known as the Pin-on-Disk was used. Load is applied by the hydraulic servo valve controlling the pressure of the hydraulic cylinder. The results showed that the rotational speed of the shaft, the operating temperature, and the discharge pressure significantly influenced the friction force between the vane and the rolling piston.

• 소성∙가공
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• 제20권3호
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• pp.243-249
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• 2011

In this study, an approach designed to compute high temperature friction coefficients for SCM 435 steel through a pilot hot rolling test and a finite element analysis, is proposed. Single pass pilot hot flat rolling tests with reduction ratios varying from 20 to 40% were carried out at temperatures ranging from 900 to $1200^{\circ}C$. In the proposed approach, the friction coefficient is calculated by comparing the measured strip spread and the roll force with the simulation results. This study showed that the temperature and reduction ratio had a significant influence on the friction coefficient. As both material temperature and reduction ratio become higher, the friction coefficient increases monotonically. This finding is not in agreement with the Ekelund model, which is widely used in the analysis of the hot rolling process. In the present work, the friction coefficient at a reduction ratio of 40% was found to be 1.2 times greater than that at a reduction of 30%. This higher friction coefficient means that an increment of the roll thrust force is expected at the next stand. Therefore, a roll pass designer must understand this phenomenon in order to adjust the reduction ratio at the stands while keeping the driving power, the roll housing structure and the work roll strength within the allowable range.

• 한국가스학회지
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• 제10권2호
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• pp.27-32
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• 2006

본 논문은 다수의 볼과 접촉하는 두개의 실린더 사이에서 발생하는 접촉응력과 마찰력을 유한요소법으로 해석하였다. LPG 충전기는 구름마찰 운동을 위해 다수의 볼이 평행한 두개의 실린더와 경사진 두개의 실린더 레이스에서 구름마찰 운동을 한다. FEM 해석결과에 의하면, SiC 볼과 SUS 304 볼은 주어진 수직하중, 즉 압축력에 대하여 높은 접촉응력과 마찰력 손실을 보여주고 있다. 반면에 PEEK 볼을 두개의 실린더에 대하여 구름마찰 운동을 유지하면, 대단히 낮은 접촉응력과 마찰력 손실을 나타내는 것으로 보아 폴리머 소재의 사용은 저마찰 접촉특성을 잘 구현하고 있다할 수 있다. 여기에 두개의 실린더가 평행하게 구름마찰 접촉운동을 하느냐, 또는 경사진 상태에서 구름마찰 운동을 하느냐에 따라 접촉거동 특성이 크게 달라지므로 특히 두개 실린더 사이의 상대적 경사도는 극도로 억제되어야 우수한 설계가 된다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1782-1793
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• 2008

Republic of korea has begun operating high speed train service according as KTX service operation starts in 2004. Also, EMU whose maximum speed is over 150 kph will be starting to service with electrification and improvement of existing railroad. Moreover, metropolitan electric railways have begun an express service to increase scheduled speed. Therefore, running resistance of rolling stock becomes more important factor effects on the performance. Running resistance of rolling stock is the factor which is necessary for the performance or operation plan of rolling stock, and it's related to rolling friction, slip friction, drag force, gradient, acceleration, curvature, tunnel condition and so on. It is possible to be calculated by CFD (Computational Fluid Dynamics). However it is predicted by experimental equation from running resistance test because of the complex calculation and manifold variables. In this paper, studies about running resistance of rolling stock is introduced, and each term of experimental equation is studied through theoretical approximation. Also, running resistance of rolling stock is estimated by the result of running resistance test, and effects being related to friction, drag force, gradient is examined.

• 소성∙가공
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• 제3권1호
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• pp.63-83
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• 1994

In this paper, the slab method have been applied to investigate the strip casting process in which hot coil is produced from molten steel directly. In the twin roll strip casting process, molten steel supplied by the nozzle cools and solidifies due to the heat extraction effect of the rolls and hot rolling of the solidified shell takes place simultaneously. The analysis of hot rolling has been carried out by using the existing results of solidification analysis for the twin roll strip casting process. The current slab method provides basic design data such as roll separation force, rolling torque, rolling power as well as end dam separation force which are required to design strip caster. The effect of friction on the basic process parameters are investigated also. It is shown that the use of appropriate friction coefficient is important and that the characteristics of hot rolling in the twin-roll strip casting process is quite different from the conventional hot rolling processes.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.308-312
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• 1999

Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

• 대한기계학회논문집
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• 제14권3호
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• pp.554-570
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• 1990

본 연구에서는 동적인 상태에서 구름접촉 거동을 좀더 명확히 하기 위해서 마 찰의 발생기구가 탄성이력손실에 기인한다는 이론을 기초로 압축 코일스프링을 이용한 감쇠자유진동시스템으로 구성된 실험장치에 의해서 구의 직경, 수직하중, 평면만의 표 면거칠기를 변화시켜 구름접촉면의 감쇠특성을 검토하고 이로부터 구름마찰력과 대수 감쇠율을 구한 다음 대수감쇠율과 진폭의 관계를 이용해서 실험에 의한 새로운 접촉폭 산출방법을 제시하고 Hertz이론에 의한 접촉폭과 마찰이론의 역학적 해석에 의한 접촉 폭과 비교, 분석해 보았다.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.85-89
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• 2007

Linear ball guideways have been used recently in precision or ultra-precision positioning devices. However, when the inner balls begin to roll or the moving direction reverses, these guideways are subject to rolling friction or nonlinear spring behavior. An ultra-precision device with a linear motor, referred to as a 'tunnel actuator' (TA), has been constructed to measure these phenomena. The application of a TA is beneficial for two reasons: it mostly cancels the attractive magnetic force between the stator and mover (armature), and its magnetic flux leakage is very low. The influence of the nonlinear spring behavior in ball guideways was investigated in this study using the pure driving force from a TA. The equilibrium between the driving force from the TA and the nonlinear spring force provided great accuracy for a positioning stage using a linear ball guideway.