Measurement of Air Gap of 30 to 50 Micron Width by Conventional X-Ray Machine

Detection of very fine defects in the width range of a few microns is very difficult by using conventional radiographic equipment, due to three limiting factorscontrast, definition and image graininess. Variables, such as X-ray energy, scattered radiation, type of film, processing parameters, film density, focal spot size, source to object distance etc, if controlled properly, can lead to radiographic image with improved quality and better flaw detection sensitivity. Image quality can be enhanced further by using microfocus X-ray tube having focal spot size from 1 to 50 micron. Microfocus X-ray machine when employed with projection radiography and real time radiography can result in ease of viewing a magnified image instantaneously. It becomes a very powerful tool for detecting microvoids and fine cracks in different materials and components having simple as well as complex geometry. However, due to high capital cost and requirement of dynamic vacuum for X-ray tube, microfocus equipments are used only in R&D sector and are rather less popular among common users. Considering the basic principles of image quality enhancement, potential of conventional X-ray machine was explored to detect the air gap of 30 to 50 micron width in a component called as “Diaphragm Type Self-Shorting Sensors”. Sensor is a tiny component having brass tube of 2mm diameter and length between 12mm to 30mm. Air gap between end cap and centrally fixed copper wire is very critical, as it controls the time lag of the measurement. Dimensional gauging of the air gap detected on the radiograph was carried out using profile projector under 20x magnification. During validation of the measuringtechnique it was observed that the total un-sharpness of the radiographic image had negligible effect on the accuracy of the measurement. Till now more than 200 sensors have been radiographed and results are quite encouraging. This paper presents the complete details of the technique developed at Centre for Design and Manufacture (CDM) for dimensional gauging of the air gap in Self-Shorting Sensors, using conventional X-ray machine.