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1.
Materials (Basel) ; 15(2)2022 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-35057242

RESUMO

Cryogenic technique is the use of a cryogenic medium as a coolant in machining operations. Commonly used cryogens are liquid nitrogen (LN2) and carbon dioxide (CO2) because of their low cost and non-harmful environmental impact. In this study, the effects of machining conditions and parameters on the wear mechanism were analysed in the milling process of AISI 4340 steel (32 HRC) under cryogenic conditions using a multilayer coated carbide cutting tool (TiAlN/AlCrN). A field emission scanning electron microscope with energy-dispersive X-ray analysis was used to examine the wear mechanisms comprehensively. At low machining parameters, abrasion and adhesion were the major wear mechanisms which occurred on the rake face. Machining at high machining parameters caused the removal of the coating material on the rake face due to the high temperature and cutting force generated during the cutting process. In addition, it was found that continuously adhered material on the rake face would lead to crater wear. Furthermore, the phenomenon of oxidation was also observed when machining at high cutting speed, which resulted in diffusion wear and increase in the crater wear. Based on the relationship between the cutting force and cutting temperature, it can be concluded that these machining outputs are significant in affecting the progression of tool wear rate, and tool wear mechanism in the machining of AISI 4340 alloy steel.

2.
Int J Occup Saf Ergon ; 22(3): 389-98, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27173135

RESUMO

INTRODUCTION: This review describes standardized ergonomics assessment based on pen-and-paper observational methods for assessing ergonomics risk factors. OBJECTIVE: The three main objectives are to analyze published pen-and-paper observational methods, to extract and understand the risk levels of each method and to identify their associated health effects. METHODOLOGY: The authors searched scientific databases and the Internet for materials from 1970 to 2013 using the following keywords: ergo, posture, method, observational, postural angle, health effects, pain and diseases. Postural assessments of upper arms, lower arms, wrists, neck, back and legs in six pen-and-paper-based observational methods are highlighted, extracted in groups and linked with associated adverse health effects. RESULTS: The literature reviewed showed strengths and limitations of published pen-and-paper-based observational methods in determining the work activities, risk levels and related postural angles to adverse health effects. This provided a better understanding of unsafe work postures and how to improve these postures. CONCLUSION: Many pen-and-paper-based observational methods have been developed. However, there are still many limitations of these methods. There is, therefore, a need to develop a new pen-and-paper-based observational method for assessing postural problems.


Assuntos
Ergonomia/métodos , Postura , Humanos , Doenças Musculoesqueléticas/prevenção & controle , Doenças Profissionais/prevenção & controle , Fatores de Risco
3.
Materials (Basel) ; 7(12): 7706-7721, 2014 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-28788270

RESUMO

The significant increase in metal costs has forced the electronics industry to provide new materials and methods to reduce costs, while maintaining customers' high-quality expectations. This paper considers the problem of most electronic industries in reducing costly materials, by introducing a solder paste with alloy composition tin 98.3%, silver 0.3%, and copper 0.7%, used for the construction of the surface mount fine-pitch component on a Printing Wiring Board (PWB). The reliability of the solder joint between electronic components and PWB is evaluated through the dynamic characteristic test, thermal shock test, and Taguchi method after the printing process. After experimenting with the dynamic characteristic test and thermal shock test with 20 boards, the solder paste was still able to provide a high-quality solder joint. In particular, the Taguchi method is used to determine the optimal control parameters and noise factors of the Solder Printer (SP) machine, that affects solder volume and solder height. The control parameters include table separation distance, squeegee speed, squeegee pressure, and table speed of the SP machine. The result shows that the most significant parameter for the solder volume is squeegee pressure (2.0 mm), and the solder height is the table speed of the SP machine (2.5 mm/s).

4.
ScientificWorldJournal ; 2013: 935981, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24222756

RESUMO

Six parents of Jatropha curcas were crossed in half diallel fashion, and the F 1s were evaluated to determine the combining ability for nine germination parameters. The ratio between general combining ability (GCA) and specific combining ability (SCA) variances indicated preponderance of additive gene action for all the characters except germination percentage, time of 50% germination, seedling length, and seedling vigor index. The parents P 1 and P 2 were the best general combiner for most of the characters studied. The cross P 1 × P 5 was the best specific combiner for speed of emergence, germination percentage, germination energy, germination index, and seedling vigor index, the cross P 2 × P 5 for mean germination time, time of 50% germination, and seedling length, and the cross P 4 × P 5 for number of days to first germination. The germination percentage varied from 58.06 to 92.76% among the parents and 53.43 to 98.96% among the hybrids. The highest germination (98.96%) was observed in hybrid P 2 × P 4, and none of the hybrids or parents showed 100% germination. The highest germination index (GI) and seedling vigor index (SVI) were found in hybrid P 1 × P 5 and P 2 × P 5, respectively. The results of this study provide clue for the improvement of Jatropha variety through breeding program.


Assuntos
Germinação/genética , Jatropha/genética , Característica Quantitativa Herdável , Jatropha/crescimento & desenvolvimento , Jatropha/fisiologia , Plântula/crescimento & desenvolvimento
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