Wear of Diamond-impregnated Bit in Drilling Engineering Ceramic
This paper describes experimental results using a scanning electron microscope (SEM) to observe the face of diamond-impregnated bit after its drilling engineering ceramic. Wear patterns and mechanisms were analyzed. The results show that several diamond wear patterns are found in the bit face including complete crystal shape, micro fragmentation, extensive fragmentation, whole fragmentation, wearing flat and particle shattered, bond abrasion mainly is in the form of shifting sand pattern, alternating thermal stress and mechanical stress are the main reasons which lead to the diamond wear, extrusion force, friction as well as abrasive debris erosion result in the shifting sand pattern of the bond.
Study on the diamond tool drilling of engineering ceramics
Abstract A method for drilling holes in engineering ceramics by using a diamond tool has been developed. In this method, a drilling tool rotates with fixed abrasives. The machining mechanism of drilling based on the fracture mechanics concept is analyzed, and a new theoretical model of the material removal rate is proposed. According to this model, the material removal rate increases in accordance with the increase of the static load applied, the rotational speed of the drilling tool, and the grain size of the abrasive. Selecting 99.5% Al2O3 ceramics as the workpiece material, experiments have been carried out. The results show that diamond drilling is an effective method for machining engineering ceramics.
Mottle on computed radiographs of the chest in pediatric patients.
PURPOSE
To investigate the relationship between radiation exposure and perceived mottle at bedside pediatric chest examinations performed with screen-film and computed radiographic techniques.


MATERIALS AND METHODS
In a pediatric intensive care unit, chest radiographs were obtained with both computed radiography (60 radiographs) and a 600-speed screen-film system (14 radiographs). The relative radiation exposure was estimated by using the sensitivity value obtained in the processing of each computed radiograph. Five radiologists assessed the mottle present in the computed radiographs and screen-film images.


RESULTS
For computed radiographs, the perceived level of mottle was inversely related to radiation exposure. For the same radiation exposure, the perceived mottle on computed radiographs was significantly higher than that on screen-film images (P < .001 for small cassettes; P < .01 for large cassettes).


CONCLUSION
Pediatric computed radiography of the chest requires approximately twice the exposure of a 600-speed screen-film system to attain the same level of mottle.