• Smart Structures and Systems
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• 제24권3호
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• pp.293-301
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• 2019

Bolted joints are commonly used in civil infrastructure and mechanical assembly structures. Monitoring and identifying the connection status of bolts is the frontier problem of structural research. The existing research is mainly on the looseness of a single bolt. This article presents a study of assessing the loosening/tightening health state and identifying the loose bolt by using ultrasonic guided wave in a bolt group joint. A bolt-tightening index was proposed for evaluating the looseness of a bolt connection based on correlation coefficient. The tightening/loosening state of the bolt was simulated by changing the bolt torque. More than 180 different measurement tests for total of six bolts were conducted. The results showed that with the bolt torque increases, value of the proposed bolt-tightening index increases. The proposed bolt-tightening index trend was very well reproduced by an analytical expression using a function of the torque applied with an overall percentage error lower than 5%. The developed damage index based on the proposed bolt-tightening index can also be applied to locate the loosest bolt in a bolt group joint. To verify the effectiveness of the proposed method, a bolt group joint experiment with different positions of bolt looseness was performed. Experimental results show that the proposed approach is effective to detect and locate bolt looseness and has a good prospect of finding applications in real-time structural monitoring.

• Structural Engineering and Mechanics
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• 제46권6호
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• pp.843-852
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• 2013

This paper presents results of the effect of different bolt tightening sequences and methods on the performance of gasketed bolted flange joint using nonlinear finite element analysis. Bolt preload scatter due to elastic interactions, flange stress variation and bolt bending due to flange rotation and gasket contact stress variation is difficult to eliminate in torque control method i.e. tightening one bolt at a time. Although stretch control method (tightening more than one bolt at time) eradicates the bolt preload scatter, flange stress variation is relatively high. Flange joint's performance is compared to establish relative merits and demerits of both the methods and different bolt tightening sequences.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.333-338
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• 2000

This paper presents an experimental study and numerical thermal deformation analysis in the home appliance, Video Cassette Recorder. Analyzing the change axial force of a set screw according to the change of temperature in the drum assembly, we can determine the initial torque in tightening set screw. The torque will have the preload boss not be separated from the bearing. Also we conduct the fundamental experiment to constitute a boundary condition of the numerical analysis. With the result of this study, we can change the material of preload boss, copper, for aluminum.

• 한국화재소방학회논문지
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• 제30권4호
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• pp.46-58
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• 2016

본 연구는 스프링클러설비용 소방용 합성수지배관에서 누수원인으로 예측되는 과도 조임에 따른 밸브 소켓 나사부의 영향을 분석하기 위하여 컴퓨터 시뮬레이션을 이용하여 밸브소켓 체결토크가 $10{\sim}130N{\cdot}m$일 때 나사부에 걸리는 응력, 변형률, 변위, Von mises stress 및 수밀용 고무패킹에 걸리는 압축응력을 예측하였으며, 이를 검증하기 위하여 토크미터를 이용한 체결토크별 접속 나사산 수, 밸브소켓과 고무패킹의 변형상태 및 수격실험을 실시하여 적정한 체결토크 값과 고무패킹 압축응력 값을 연구하였다. 본 연구 결과가 소방용 합성수지배관 누수방지를 위한 관련 규격 또는 기술기준 개정에 필요한 자료로 활용될 수 있도록 기대한다.

• 대한치과보철학회지
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• 제34권1호
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• pp.1-14
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• 1996

Abutment screw loosening of dental implant is a major problem in the treatment of dental implant. The purpose of this study was to examine the effect on the prevention of screw loosening according to tightening method and using of washer. In the first experiment, using a implant fixture and precisely fabricated temporary cylinder, the loosening torque was measured by tightening the screw 5 times repeatedly. In the second experiment, the fabricated crown and implant fixture was tightened by the screw that is attatched washer and then the loosening torque was measured after loading it 1800, 12600 times under the force of 150N. The results were as follows. 1. The highest loosening torque appeared after tightening 3 times repeatedly(p<0.01). 2. When the washer was used, the loosening torque was increased significantly under the loading 1800 times(p<0.01), 3. When the washer was used, the loosening torque was increaed under the loading 12600 times, but it is statistically not significant(p<0.01). The first experiment results mean that 3 times repeated tightening screw is most effective clinically. The second results mean that washer is effective in prevention screw loosening, but the effect is decreased with increasing load.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 추계학술대회 논문집
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• pp.619-620
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• 2009

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.312-316
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• 1987

A simple hybrid circuit to control the two-phase AC motor of the nut-runners which employ the tightening torque control system is described in this paper. The circuit has emphasis on the low-cost implementation. The circuit constitutes of the V/F converter using a timer IC, the pulse width modulator using the fastening torque signal and the two-phase logic sequencer.

• 대한치과보철학회지
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• 제46권4호
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• pp.396-408
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• 2008

연구목적: 임플랜트 치료에서 가장 흔히 발생하는 기계적 문제점 중 하나는 나사의 풀림이다. 지대주 나사에 조임회전력을 가하는 목적은 나사를 신장시켜, 신장된 나사의 인장력에 의한 지대주와 고정체간의 압축력을 통해 연결부의 안정성을 부여하는 데 있다. 조임 회전력의 결과로 나타나는 전하중의 크기는 다양한 요소에 의해 영향을 받기 때문에, 동일한 조임회전력을 적용하였다 할지라도 임플랜트 시스템의 종류에 따라 전하중의 크기가 달라질 수 있다. 따라서 지대주 나사 연결부의 안정성을 위한 다양한 임플랜트 시스템의 적정 조임회전력 크기에 관한 연구가 필요하다. 본 연구에서는 external butt joint와 두 가지 internal cone 연결형태를 갖는 임플랜트 시스템들에서 지대주 나사의 조임회전력이 임플랜트-지대주 나사 연결부의 안정성에 미치는 영향을 하중 전후의 풀림회전력 측정을 통해 알아보고자 하였다. 연구재료 및 방법: External butt joint 형태를 가지는 US II 시스템과 $8^{\circ}$ internal cone 연결형태의 SS II 및 $11^{\circ}$ internal cone 연결형태의 GS II 시스템에서 20 Ncm, 30 Ncm, 그리고 40 Ncm의 각기 다른 조임회전력을 적용한 후 초기 풀림회전력 및 상실률과 $10^5$회의 반복하중 후의 풀림회전력 및 상실률을 비교 분석하였다. 연구결과 및 결론: 1. 초기 풀림회전력과 하중 후 풀림회전력은 조임회전력의 크기가 증가할수록 크게 나타났다 (P < .05). 2. 초기 풀림회전력 상실률은 SS II 시스템에서는 조임회전력 크기에 따른 차이가 없었으나 (P > .05), GS II와 US II에서는 20 Ncm 보다 40Ncm의 조임회전력에서 더 낮게 나타났다 (P < .05). 3. 하중 후 풀림회전력 상실률은 세 시스템 모두 30 Ncm의 조임회전력을 가했을 때 가장 낮게 나타났다 (P < .05). 4. 하중 후 풀림회전력 상실률은 SS II, GS II, 그리고 US II 순으로 높아지는 경향을 보였다. 5. 초기 풀림회전력과 하중 후 풀림회전력 상실률 간에는 상관관계가 없었다 (P > .05). 이상의 결과로부터 임플랜트 시스템의 종류뿐만 아니라 조임회전력의 크기 또한 지대주 나사의 풀림회전력 상실에 영향을 준다는 것을 알 수 있다. 따라서 임플랜트-지대주 나사 연결부 안정성 유지를 위해서는 임플랜트 시스템마다 적정 조임회전력이 제시되어야 하고, 또한 임상에서 이를 준수하는 것이 매우 중요하다고 생각된다.

• Journal of Korean Dental Science
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• 제2권1호
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• pp.19-27
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• 2009

Tightening of the screws in implant restorations should be accurate and precise. If applied torque is too low, screw loosening would be occurred. With too high torque, the screw fracture might take place. Various torque generating devices are developed and employed to apply a proper torque. The purpose of this investigation was to determine and compare the accuracy of the torque controllers. In this study, 4 types of torque controllers were used; electronic torque controller, torque limiting device, torque indicating device and contra angle torque driver. Digital torque gauge was employed to measure the de-torque value. Thirty cycles of tightening and loosening were done with each torque controller. All implant torque controllers have shown slight errors and deviations. The torque liming device exhibited the most accurate data. No significant difference was found among the mean de-torque values of the electronic torque controller, torque indicating device and contra angle torque driver. In the limitation of this study, it would be recommended that the implant torque controllers should be checked whether uniformed and precise torque can be generated and a measuring error should be corrected.

• Industrial Engineering and Management Systems
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• 제10권3호
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• pp.209-220
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• 2011

Self-tapping screws have some operational peculiarities. In spite of their economical advantage that requires no prior tapping operation, a weakness of self-tapping screw-tightening operations is that screws can easily be tightened at a non-right angle, thus resulting in an improper tightening strength. Increases in outsourced workers have reduced labor costs, but the accompanying high worker fluidity means that new workers are more frequently introduced into factories. It is necessary to train new workers for self-tapping screw-tightening operations, which occupies a considerable portion of ordinary assembly works. The purpose of this study is to develop and implement a skill transfer system for the operation. This study (1) proposes a set of characteristic values for evaluating the quality of the operation and develops a device that can measure these values; (2) proposes criteria for evaluating the resultant quality of the tightening; and (3) develops a skill training system for better work performance. Firstly, sets of characteristic values for evaluating the quality of the operation, namely, torque, vertical pressure forces and horizontal vibration forces, are proposed. A device that can measure these values is developed. Secondly, criteria for evaluating the resultant quality of the tightening are identified, involving tightening torque, maximum vertical pressure and timing, vibration area during the processing and tightening period, and work angle. By using such parameters, workers with the proper aptitude can be identified. Thirdly, a skill training system for the operation is developed. It consists of screwdriver operation training and screw-tightening training with feedback information about the results of the operation. Finally, the validity of the training system is experimentally verified using new operators and actual workers.