Abrasive grit blasting parameters

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Abrasive grit blasting is used quite extensively both in metal finishing industries as well as in the general fabricating and outdoor fields. Limiting ourselves to the abrasive grit blasting used in metal finishing industries, one would be interested in the controlling parameters of the process. Only when the necessary parameters for abrasive grit blasting are first of all identified, can they then be controlled. And only when you have a controlled set of parameters, can you ensure a consistent surface morphology that can be repeated over and over again in order to ensure quality from batch to batch and from part to part.

So what are the abrasive grit blasting parameters that can be identified for control? The correct answer is that there are too many of them to go into very great detail in one post. However, limiting ourselves only to pneumatic abrasive grit blasting and limiting ourselves only to operations performed in a controlled grit blast cabinet, we can identify a few key items here. Of course, more discussions on this topic will always be the subject of future posts.

The first and foremost parameter is the air pressure. This pressure usually given in pounds per square inch is the controlling force parameter. Excessive pressure or very low pressure are both to be avoided and a reasonable upper and lower limit needs to be established. The second parameter is the stand-off distance. This is the distance, usually given in inches, between the nozzle and the work surface. Too high or too low stand-off distances are both to be avoided. The next parameter is the blast gun movement speed. If the grit blasting gun is moved too rapidly, then the necessary profile will not be achieved; conversely, if the grit blasting gun dwells on any one place too long or moves too slowly, then the metal peaks will get folded on to themselves resulting in a poor surface roughness again. Hence there is an optimum speed that has to be maintained and controlled.

The grit blast gun angle is another important parameter to be considered. Not all grit blasting is done at ninety degrees to the surface and so when an angle other than ninety degrees is being employed, the angle of attack of the impinging particles results in a lower force than otherwise and the surface profile will be altered. This angle that really depends upon each individual application needs to be controlled and monitored.

If the part that is being abrasive grit blasted is on a turn-table that is rotating, then the rotating speed that is usually prescribed in surface feet per minute is another important parameter that has to be controlled and monitored. An important parameter that is often overlooked is the nozzle geometry of the grit blasting nozzle itself. Many times, the nozzle diameter may have gotten eroded and therefore become larger and needs replacement, failing which the force component will change and next thing you know the quality control between batch to batch will start suffering.

Hence there are several key parameters that need to be identified and controlled in order to ensure repeatable performance in abrasive grit blast operations.