PROBLEMS RAISED BY NOXES CONTROL AT FCAW
Flux cored arc welding (FCAW) is applied due to its remarkable results and advantages (high productivity, joint quality etc) in various fields (industrial construction, naval, chemistry, petrochemistry etc.). FCAW disadvantages, mainly the emission of pollutants, can be counteracted by their rigorous control and local forced ventilation in the production. Control measures that can be used for measuring “in-situ” noxes resulting from the FCAW process are presented. Case studies are presented as well, containing data regarding two new tubular wire produced in order to be used with the flux cored arc welding process.
MECHANICAL VENTILATION IN WELDING
Mechanical ventilation is reliable. It can be more effective than natural ventilation. The main mechanical ventilations were presented: ventilations applied in working places where welding techniques as well as allied processes (brazing and spraying) are used. Adequate ventilation depends on: number and type of operations; size and shape of the workplace; type and effectiveness of the ventilation; position of the worker’s and welder’s head; contents of the fume plume. The case studies presented, as well as the afferent technical data completed the given study. 1. GENERAL PROBLEMS Mechanical Ventilation is the movement of air through a workplace by a mechanical device such as a fan. Mechanical ventilation is reliable. It can be more effective than natural ventilation. Local exhaust, local forced air, and general ventilation are examples of mechanical ventilation [1]. Adequate ventilation depends on: number and type of operations; size and shape of the workplace; type and effectiveness of the ventilation; position of the worker’s and welder’s head; contents of the fume plume [2, 3, 5]. 2. SELECTION CRITERIA FOR STATIONARY FILTER EQUIPMENT When welding metals, different sizes of dust particles are generated. The diameter of the particles is between 0,1 microns and 1,0 microns, mainly in the range under 0,4 microns. Table 1. Typical distribution of particles in welding fumes particle Ø in μm <0.2 <0.4 <0.6 <0.8 <1.0 >1.0 number 800 251 9 0 1 2 % of the number 75.3 23.6 0.9 0 0.1 0.2 % of the mass 15.9 38.7 7.5 0 8.2 29.7 Source: Spiegel-Ciobanu (AWS-study) The table shows that 98,9 % of the particles fall in the range of up to 0,4 microns. These particles are hardly removed at all by class M filters. Class ,,M" filters are not sufficient to protect the employees [6, 7] It is essential that you use state of the art technology ANNALS of the ORADEA UNIVERSITY. Fascicle of Management and Technological Engineering, Volume IX (XIX), 2010, NR2
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.