• Journal of the Korean Ceramic Society
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• v.17 no.2
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• pp.69-74
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• 1980

This study deals with the wire content, wire diameter, aspect ratio , it's arrangement of steel, wire fiber and the sorts of castable which affected the character of steel wire fiber reinformced refractory castable. Two kinds of alumina based refractory castables, one is for 1650℃ and the other is for 1800℃, and stainless steel which is SUS 304 type 0.25, 0.34 , 0.37 and 0.50m/min diameter were used respectively. Aspect ratio was adjusted to 50, 75, 100 and steel fiber content was also adjusted to 1-4wt% each. The results of the experiment were as follows : 1. At firing temperature around 1,000℃, MOR is increased with increasing wire content and aspect ratio with decreasing firing temperature, which depends on the Romualdi's Fiber Spacing Theory. But for calculation of the fiber spacing, Swamy equation is more a aplicable to the extensive fiber mixing conditions. However, the condition differs from the above at firing temperature around 1,350℃ ,because of the degradation of wire and the progress of sintering of castable. 2. Linear change is getting larger corresponding to the increase of wire content, and the spaling resistivity is increasing corresponding to the increase of wire content and to aspect ratio, and with decreasing wire diameter. 3. Firing shrinkage under load is getting greater as higher wire content, and the shrinkage of the test pieces which fiber is vertically oriented is getting greater than the test pieces which fiber is randomly oriented.

• Journal of Environmental Health Sciences
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• v.26 no.4
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• pp.21-28
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• 2000

Various man-made mineral fibers(MMMF) including refractory ceramic fiber(RCF) have been used widely in industries as insulation materials. The effect of fibrous dust on human health depends on fiber size, concentration (exposure level), and durability in biological system. Therefore, these parameters should be determined to evaluate accurately the potential risk of fibers on human health. The purpose of this study was to characterize the size of airborne fiber and the workers＇ exposure to airborne fibers in refractory ceramic fiber manufacturing and processing factories. Airborne fibers were collected on 25-mm mixed cellulose ester membrane filters at personal breathing zones, and analyzed by A and B counting rules of the National Institute for Occupational Safety and Health(NIOSH) Method # 7400. The average ratios of the fiber density by B rule to the fiber density by A rule was 0.84. This result indicates that the proportion of respirable fibers (<3 ${\mu}{\textrm}{m}$ diameter) in air samples was high. The average diameter and length of airborne fibers were 1.05${\mu}{\textrm}{m}$ and 35${\mu}{\textrm}{m}$, respectively. The average fiber concentrations (GM) of all personal samples was 0.26f/cc, and the average concentration was highest at blanket cutting and packing processes. The fifty seven percent of personal air samples was exceeded the proposed American Conference of Governmental Industrial Hygienists(ACGIH) Threshold Limit Value(TLV), i.e. 0.2 f/cc. It was concluded that the RCF industrial workers had the higher potential health risk due to small fiber diameter, long fiber length, and high exposure level to the airborne fibers.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.2
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• pp.134-139
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• 2012

Objectives: This study was conducted to study the analytical variability of A & B counting rules in counting using a phase contrast microscope airborne fibers collected on filters in man-made mineral or vitreous fibers (MMMFs) industries. Methods: Fibers in filters were counted using A & B rules of NIOSH Method 7400. Intra-counter and inter-counter variations by fiber type and density were obtained. The types of MMMFs analyzed were glass wool fiber, rock wool fiber, slag wool fiber, and refractory ceramic fibers. The densities of fibers classified were <20 $fibers/mm^2,$ 20 - <50 $fibers/mm^2$, 50 - <100 $fibers/mm^2,$ and ${\geq}100$ $fibers/mm^2,$ respectively. Results: Intra-counter relative standard deviations by rule A were 0.084, 0.102, 0.071 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.139, 0.120 and 0.142, respectively. Inter-counter relative standard deviations by rule A were 0.281, 0.296, 0.180 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.396, 0.337 and 0.238, respectively. Conclusions: Intra-counter variation was not different significantly among fiber types (p>0.05), but B rule variation for ceramic fibers approximately 2 times greater than corresponding A rule estimates, and intra-counter and inter-counter variations were higher in the low fiber density.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.287-294
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• 2012

Ceramic Matrix Composites (CMCs) represent a class of non-brittle refractory materials for harsh and extreme environments in aerospace and other applications. The quasi-ductility of these structural materials depends on the quality of the interface between the matrix and the fiber surface. In this study, a manufacture route is described where in contrast to most other processes no additional fiber coating is used to adjust the fiber/matrix interfaces in order to obtain damage tolerance and fracture toughness. Adapted microstructures of uncoated carbon fiber preforms were developed to permit the rapid infiltration of molten alloys and the subsequent reaction with the carbon matrix. Furthermore, any direct reaction between the melt and fibers was minimized. Using pure silicon as the reactive melt, C/SiC composites were manufactured with an aim of employing the resulting composite for friction applications. This paper describes the formation of the microstructure inside the C/C preform and resulting C/C-SiC composite, in addition to the MAX phases.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.213-220
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• 2005

Penetration and health effect of fibers was related with their diameters and length. The purpose of this study is to characterize and compare the diameter and length of airborne man-made mineral fibers(MMMF) or synthetic vitreous fibers in the related industries. The average fiber length of the continuous filament glass, rock wool, refractory ceramic, and glass wool fibers production industries approximately 27, 28, 35, $50-105{\mu}m$. Airborne glass fibers were longest in all the type of MMMFs. The average diameters of airborne fibers generated from refractory ceramic, rock wool, glass wool, continuous filament glass fibers production industries were approximately 1.0, 1.6, 1.5-4 and $10{\mu}m$, respectively. The percentages of respirable fibers(<$3{\mu}m$) were 94% for RCFs, 73% for rock wool fibers, 61.0% for glass fibers, and 1.6% for filament glass fibers. The length of glass fibers were the longest in all types of fibers, and length of the others were similar. The refractory ceramic fibers were smallest in diameters and highest in fraction of respirable fibers.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.9 no.2
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• pp.158-166
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• 1999

The purpose of this study was to investigate the correlation between airborne total dust and man-made mineral fibers (MMMF), and to estimate total dust concentration to maintain below the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV$^{(R)}$) for the MMMF. The regression coefficients between airborne total dust concentrations and fiber concentrations determined in the industries producing glass fibers, rock wool. refractory ceramic and continuous filament glass fibers products were 0.41, 0.42, 0.20 and 0.19, respectively. The size characteristics of fibers as well as the amounts of contaminated non-fibrous dusts could affect the correlation intensities. When total dust and fiber exposure data were compared with the occupational exposure limits, there was a large gap between two evaluation results. The regression coefficient between total dust and fiber data was increased ($r^2=0.88$) in the process of insulation installation generating in the higher levels of glass or rock wool fibers. In this case, an estimated total dust concentration of glass wool or rock wool fibers complying with the ACGIH TLV (1 f/cc) was $1.7mg/m^3$. In conclusion, the total dust and fibers concentrations was highly correlated at the higher exposure levels so that total dust-monitoring data could be used to control simply and economically and to estimate worker's exposure to fibers.

• Current Industrial and Technological Trends in Aerospace
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• v.9 no.1
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• pp.139-149
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• 2011

The combustion chamber and nozzle of a liquid rocket engine need thermal protection against the high temperature combustion gas. The nozzle extension of a high-altitude engine also has to be compatible with high temperature environment and several kinds of cooling methods including gas film cooling, ablative cooling and radiative cooling are used. Especially for an upper-stage nozzle extension having a large expansion ratio, the weight impact on the launcher performance is crucial and it necessitated the development of light-weight refractory material. The present survey on the nozzle extension materials employed in the liquid rocket engines of USA, Russia and European Union has revealed a trend that the heavier metals like stainless steels and titanium alloys are being substituted with light weight carbon fiber or ceramic matrix composite materials.