• 한국안전학회지
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• 제34권3호
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• pp.21-27
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• 2019

Many accidents have been occurring during welding and flame cutting work related to maintenance and repair as the domestic manufacturing facilities gradually become decrepit. However, it is not easy to find the accurate statistics and analysis data on accidents occurring during welding or flame cutting operations related to maintenance and repair of machinery and equipment. Therefore, in this study, the fatal accident cases of fire/explosion and asphyxiation that occurred during the welding and flame cutting work in the manufacturing industry were collected and their characteristics were analyzed. Then, we tried to find the connection of the accidents according to the machinery/equipment and the work content, and to provide the materials and measures that can be used to prevent the similar accidents. We collected 329 cases of the fatal accidents related to fire/explosion and leakage/contact of chemical substances in the domestic manufacturing industry during the last 10 years (2008 ~ 2017). Among them, 72 accidents occurred during welding or flame cutting were extracted and the related reports were investigated whether they occurred during usual work or unusual work. Also, the machinery/equipment and the work content related to the accidents were classified and analyzed based on the criteria. The analysis results showed that 31 cases of the fire/explosion accidents occurred during usual work and 32 cases during unusual work, and it was found that 9 cases of asphyxiation death occurred during usual work. Then, from the analysis results, the connections of the machinery/equipment and the work contents related to the accidents were schematized into a accident tree.

• 항공우주시스템공학회지
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• 제16권1호
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• pp.12-16
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• 2022

유도 용접은 비접촉식으로 깨끗하고 빠른 공정으로 현재 주목받고 있다. 하지만 열가소성 수지는 전자기장에 영향을 받지 않기 때문에 유도 용접은 서셉터(Susceptor)라는 발열체가 필요하다. 고품질 접합을 목표로 연구가 진행되고 있지만, 결국 발열체라는 이물질이 들어가기 때문에 기준이 필요하다. 시편의 제작과 시험은 ASTM D5868에 근거하여 진행된다. 본 논문에서 평가 기준은 용접된 접합면의 상태와 기공률, 전단강도로 총 3가지를 근거로 판단할 것을 제안한다. 용접되는 접착면은 용융되고 냉각되면서 고형화가 되기 때문에 급격한 온도 변화는 기공을 발생시킬 수 있다. 또한 가열이 균일하지 않다면 원하는 성능을 기대하기 힘들다. PA6 (CF 30%) 엔지니어링 플라스틱을 이용하여 서셉터 제작과 유도 용접 그리고 성능 검증으로 진행하였다.

• 비파괴검사학회지
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• 제36권6호
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• pp.466-473
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• 2016

선박 건조과정에서 이면부의 도장손상은 용접과정에서 과도한 입열량(heat input)에 따른 전도의 영향으로 손상 방지를 위해서는 용접온도 계측에 의한 적절한 입열량 제어가 필요하다. 온도 계측에는 접촉식, 비접촉식 방법이 있으며 열화상 시스템은 대표적인 비접촉식 방법이다. 하지만 일반적인 열화상 시스템의 탐지센서(detector)는 고온물체에서 방출되는 복사량(radiant quantity)이 과도하면 백화현상(saturation)으로 인해 온도계측이 불가능해진다. 따라서 본 논문에서는 열화상 시스템에 집속되는 과도한 복사량을 차단하기 위해 중성밀도필터(neutral density filter)를 결합하여 고온 물체의 온도를 $3000^{\circ}C$까지 정량적으로 계측하기 위한 복사 에너지 필터링을 연구하였다.

• 대한치과보철학회지
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• 제38권2호
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• pp.200-213
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• 2000

Lasers have given dentistry a new rapid, economic, and accurate technique for metal joining. Although laser welding has been recommended as an accurate technique, there are some limitations with this technique. For example, the two joining surfaces must have a tight-fitting contact, which may be difficult to achieve in some situations. The tensile samples used for this study were made from a custom-made pure titanium and type III gold alloy plates. 27 of 33 specimens were sectioned perpendicular to their long axis with a carborundum disk and water coolant. Six specimens remained and served as the control group. A group of 6 specimens was posed as butt joints in custom parallel positioning device with a feeler gauge at each of three gaps : 0.00, 0.25. and 0.50mm. All specimens were then machined to produce a uniform cross-sectional dimension, none of the specimens was subjected to any subsequent form of heat treatment. Scanning electron microscopy was performed on representative tested specimens at fractured surfaces in both the parent metal and the weld. Vickers hardness was measured at the center of the welds with a micropenetrometer using a force of 300gm for 15 seconds. Measurement was made at approximately $200{\mu}m\;and\;500{\mu}m$ deep from each surface. One-way analysis of variance (ANOVA) and Scheffe's test was calculated to detect differences between groups. The purpose of this study is to compare the strength and properties of the joint achieved at various butt Joint gaps by the laser welding of type III gold alloy and pure titanium tensile specimens in an argon atmosphere. The results of this study were as follows : 1. When indexing and welding pure titanium, there was no decrease in ultimate tensile strength as compared with the unsectioned alloys for indexing gaps of 0.00 to 0.50mm, although with increasing gap size may come increased distortion (p>0.05). 2. When indexing and welding type III gold alloy, there were significant differences in ultimate tensile strength among groups with weld gaps of 0.00mm, 0.25 and 0.50mm, and the control group. Group with butt contact without weld gap demonstrated a significant higher ultimate tensile strength than groups with weld gaps of 0.25 and 0.50mm (p<0.05). 3. When indexing and welding the different metal combination of type III gold alloy and pure titanium, there were significant differences in ultimate tensile strength between groups with weld gaps of 0.00, 0.25, and 0.50mm. However, the mechanical properties of the welded joint would become too brittle to be acceptable clinically (p<0.05). 4. The presence of large pores in the laser welded joint appears to be the most important factor in controlling the tensile strength of the weld in both pure titanium and type III gold alloy.

• 소성∙가공
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• 제7권1호
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• pp.66-71
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• 1998

The present study is concerned with the hydrostatic extrusion process of copper-clad aluminium bar to investigate the bonding conditions as well as the basic flow characteristics. Considering the bonding mechanism of bi-metal contact surface as cold pressure welding the normal pressure and the contact surface expansion are selected as process parameters governing the bonding conditions, in this study the critical normal pressure required for the local extrusion-the protrusion of virgin surfaces by the surface expansion at the interface-is obtained using a slip line method and is then used as a criteron for the bonding. A rigid plastic finite element method is used to analyze the steady state extrusion process. The interface profile of bi-metal rod is predicted by tracking the paths of two particles adja-process. The interface profile of bi-metal rod is predicted by tracking the paths of two particles adja-cent to interface surface. The contact surface area ration and the normal pressure along the interface are calculated and compared to the critical normal pressure to check bonding. It is found that the model predictions are generally in good agreement with the experimental observations. The compar-isons of the extrusion pressure and interface profile by the finite element with those by experi-ments are also given.

• 한국정보통신학회논문지
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• 제5권1호
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• pp.144-149
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• 2001

산업현장의 열악한 작업중의 하나인 용접작업을 자동화하기 위한 방법으로 본 논문은 비접촉식 센서인 Fiber Sensor를 이용하여 용접선을 1차적으로 추적하고, 추적한 데이터를 텍스트 파일로 저장함과 통시에 2차적으로 추적한 용접선을 X-Y 로봇의 좌표값으로 다시 출력하여 용접을 하도록 하고 있다. Fiber Sensor를 통하여 읽어 들인 데이터는 Delphi Version 3.0을 이용하여 만들어진 프로그램을 통하여 처리하였고, I/O 입출력은 16 채널의 Relay Actuator 출력과 16 채널의 opto-isolated 입력이 가능한 PC의 ISA슬롯에 직접 삽입하여 사용하는 카드를 통해서 이루어졌다. 본 실험에서 용접선 추적은 직선, 기울기를 가진 직선 및 곡선에 관하여 추적을 행하였고, 추적한 데이터를 토대로 인버터 $CO_2$ 용접기를 사용하여 용접을 행하여 보았다.

• 한국표면공학회지
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• 제44권2호
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• pp.50-54
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• 2011

Hydrophobic a-C:F film was coated on polycarbonate film with $CF_4$, $C_2F_6$ and HFC ($C_2F_4H_2$) gas in helium discharge generated by 5~100 kHz AC power supply at atmospheric pressure and room temperature. The highest water contact angle of the a-C:F film formed with $He/C_2F_6$ mixed gas is $155^{\circ}$. X-ray photoelectron spectrum showed that there was 40% of C-$CF_3$ bond at the surface of the super hydrophobic film. The contact angle and deposition rate were decreased with increasing substrate temperature. The contact angle was generally increased with the surface roughness of the film. The contact angle was high when the surface microstructure of the film was fine and sharp at the similar roughness and chemical composition of the surface.

• 한국기계가공학회지
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• 제19권12호
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• pp.80-86
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• 2020

With the exception of welding activities, it is forbidden to use electricity in shipyards, owing to safety concerns such as the possibility of fire, explosions, and short circuits. In this paper, an automatic chamfering machine using pneumatics is proposed for use in such environments. Customers specify their requirements and the machine derives the corresponding theoretical design conditions. The proposed machine was used to perform 3D modeling, and its suitability and performance were confirmed via cutting experiments of the manufactured device. Two types of sensors may be used in this system: contact and non-contact. In the case of the contact type, an end-stop switch that can recognize the end of the material is installed, and when the machine reaches the end of the material, the end-stop switch is operated to cut off the air pressure. In the non-contact type, four sensors were used: photonic, ultrasonic, metal detection, and encoder. The use of the four sensors was repeated 30 times, and the average error determined. Thus, the optimum sensor was identified.

• 한국철도학회논문집
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• 제15권6호
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• pp.597-603
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• 2012

본 연구에서는 바이어스 궤도계전기의 접점재료를 선정하는데 있어 Ag 접점과 AgC 접점의 문제점을 분석하고, 안전성을 평가하는데 목적이 있다. 접점의 용착실험과 반복개폐 실험을 실시하여 접점의 특성을 알아보았다. 실험 결과, Ag 접점은 비교적 낮은 전류에서 용착이 발생하였고, AgC 접점은 온도특성이 우수하여 대전류에서도 용착이 발생하지 않았다. 반복개폐 실험에서는 AgC 접점의 개폐횟수가 증가할수록 저항이 불안정하고 접점에 전이현상이 발생하여 접점소모가 큰 것으로 나타났다. 연구 결과, AgC 접점은 용착특성에서는 우수하나 반복개폐 실험에서 저항변화가 많아 사용상 주의가 요구되며, Ag 접점은 반복개폐 특성은 우수하나 용착특성에서 취약한 것으로 나타났다.

• 전기전자학회논문지
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• 제25권1호
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• pp.95-100
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• 2021

조선소에서 선체 블록과 용접 피더의 위치를 알면 작업자의 위치 정보를 쉽게 얻을 수 있다. 이 데이터는 작업장 안전 모니터링 시스템 구축에 매우 유용하다. 그러나 선체 구조와 용접 공정의 특수성 때문에 작업장에 고정 통신망을 적용하기 어렵다. 본 연구에서는 전용 통신선을 대신할 수 있는 유도 전력선 통신을 선체블록과 같은 금속매체에 적용하는 기술을 검토하였다. 용접기의 전원 케이블에 설치할 유도 결합기로 페라이트 코어를 사용하였고, 금속 블록의 지지대에 체결할 결합기로 나노 결정질 코어를 적용하였다. 제안된 커플러는 COMSOL AC/DC 모듈로 3차원 모델링 하였고 동작 원리를 시각화하기 위하여 유한 요소 해석을 수행하였다. 알루미늄 프로파일을 사용한 금속블록 통신 성능 테스트에서 용접 전극의 블록 접촉으로 통신 채널이 형성되었을 때 대역폭은 6 Mbps 이상 유지되었다.