Research project 1 of the metal spraying and coating Division of the Institute of Welding: progress report no. 1

Introduction The quality of a sprayed metal deposit is known to be related to the nature of the prepared surface of the base metal. Grit blasting is a common method of surface preparation, and the actual profile or surface contour of the prepared surface can be varied considerably by variation in blasting conditions. The exact requirements of an acceptable surface have never been accurately stated, although a degree of undercut is. considered essential. The object of the present work is to develop a non-destructive method for the assessment of blasted mild steel surfaces in terms of suitability for metal spraying. Such a method needs to combine simplicity and speed, so that it can be used by normal inspection personnel without delaying production. Preferably the method should incorporate a 'failsafe! mechanism.. A number of possible assessment methods have been considered, but attention has been largely concentrated on measurement of the diffuse reflectivity of blasted surfaces. In reality, of course, this is simply an attempt to replace the eye in visual inspection with an instrument, and so remove the human element. Results have been reasonably encouraging, but it is obvious that many more samples need to be examined before a true judgement can be made. Some difficulty has been encountered in deciding the requirements for an acceptable surface. For this reason, a part of the experimental effort has been devoted to the examination of blasted surfaces, and to the measurement of bond strength after metal spraying. A brief review of literature has also been included.